We have spoken before, here and here, about so-called "use-it-or-lose-it entitlements".
The catalyst behind this idea -- and it is just an idea at this stage, at least here -- is the belief that too many developers are sitting idle on zoned land. And they're allegedly doing this because they believe it will be worth more tomorrow.
Why bother building anything when you can instead just wait and make money that way?
To counteract this speculative force, some believe that one answer is to just strip land of its zoning entitlements if it's not used within a certain period of time (right now it lasts forever). I get why this is sometimes proposed, but my response to this has consistently been: it's a terrible idea.
It is a terrible idea because developers are generally always incentivized to move as quickly as possible. And it is a terrible idea because every now and then a period in the cycle will arrive where, it's not that developers don't want to build, it's that many/most can't.